In recent years, virtualization technology that makes it possible to operate a plurality of Operating Systems (OS) on a physical machine has been widely used. For achieving a virtual machine, there is a method wherein a layer is created in the OS (host OS) that operates on a typical physical machine for operating a virtual machine, and there is a method of creating a layer (hypervisor) on the hardware for operating a virtual machine without going through the host OS, and operating a guest OS on that layer.
Japanese Patent No. 4,468,426 discloses a method of collecting synchronization information that was generated for a first virtual machine and that relates to an event that accompanies input to the first virtual machine, and controlling the execution state of the input of a second virtual machine according to that synchronization information so that it is the same as the execution state of the input of the first virtual machine.
Japanese Patent Application No. 2009-080692 discloses a method wherein, when failure occurs in a server computer on which a virtual machine is operating, the virtual machine is reproduced on another server computer based on a snapshot that was obtained by a disk drive at the closest point in time to the time when the failure occurred. This snapshot is CPU context of the computer that is operating and data inside the memory for processing that is used when that CPU is operating, and data inside the disk drive that is extracted at predetermined timing (check point).
Japanese Patent Application No. 2008-033483 discloses a method wherein, when failure occurs, the list of files included in a copy image on the disk of a first computer and the execution context of the computer are copied to a second computer, that list of files is then referenced in order to copy the copy image from the disk of the first computer to the disk of the second computer.